The present invention concerns axial locking of a valve shaft to be non-turnably attached to a closing element of a valve, wherein an end of the shaft to be attached to the closing element has been machined on two opposite sides to fit into a pivot recess formed in the outer perimeter of the closing element.
Since overpressure is predominant in the valve housing, the valve shaft tends to push out from the valve housing in the axial direction. To prevent this from occurring, various solutions have been devised that succeed in preventing the valve shaft from pushing out from the valve housing in the axial direction, but these either require a lot of components and difficult additional working phases or the manufacture of them is uneconomical in terms of material consumption. Further, with these solutions, assembling of the valve requires additional arrangements in the structure of the valve housing which can, in turn, cause additional problems.
One known locking solution is based on the use of a shouldered shaft. When fabricating such a shaft the billet used has to be at least as thick as the diameter of the shoulder. This solution is uneconomical in terms of material consumption. In addition, mounting of such a spindle into the valve requires special arrangements in the valve housing, which further increases the manufacturing costs and the risk of leakage. According to one alternative, the valve housing is provided with a cover sleeve which is slid upon the shaft from the outside, for which cover sleeve, the valve housing has to be provided with an opening having a seal, onto which opening the cover sleeve is fastened by screws. This solution increases the manufacturing costs considerably and increases the risk of leakage of the valve. In an alternative, somewhat more economical solution, the valve housing is provided with a bottom plug, through which the shouldered valve shaft is mounted in place. The solution utilizing a bottom plug also increases manufacturing costs and the risk of leakage.
Further, a solution has been proposed wherein a shouldered valve shaft is made sufficiently short for mounting via a port. Hereby no additional openings are necessary in the valve housing itself, but a shaft coupling and an extension part increasing the costs must be installed on the outer end of the valve shaft. This solution causes looseness of the shaft structure, which has negative effects on the operation of the valve, especially if the valve shaft is coupled to a sensitive control device.
According to another solution for axial locking of a valve shaft, a locking part is slid onto the top of the shaft after the end of the valve shaft has been passed into the valve housing via a borehole for the shaft, the locking part being locked in place by means of a closure pin. The closure pin is an additional part of the structure, further requiring a transversal through hole in the end of the shaft and in the locking part. All this increases the manufacturing costs, which circumstance is of importance especially in mass production.